data2mat <-
  function(data = data) {
    if (!any(colnames(data) == "abundance")) {
      stop("A column named \"abundance\" must be speciefied.")
    }
    if (!any(is.integer(data$abundance))) {
      stop("Number of individuals must be integer!")
    }
    col <- which(colnames(data) == "abundance")
    data1 <- data[, -col]
    abundance <- as.numeric(data[, col])
    result1 <- data.frame(rep(NA, sum(abundance)))
    colnames(result1) <- "plots"
    for (i in 1:(ncol(data) - 1)) {
      result1[, i] <- rep(as.character(data[, i]), abundance)
    }
    result <- table(result1)
    return(result)
  }
